The present invention relates to a process for the production of furnace black.
Furnace blacks are produced in large quantities in carbon black reactors for a wide variety of industrial applications. Carbon black reactors generally consist of combustion chambers, mixing chambers and reaction chambers arranged along the axis of the reactor, which are connected with each other and form a flow path for the reaction media from the combustion chamber through the mixing chamber to the reaction chamber. In the combustion chamber a fuel, normally gas or oil, is burned with the aid of a burner with the addition of pre-heated combustion air, to produce a high temperature. A mostly liquid, carbon-containing raw material, for example a black oil, is sprayed into the hot combustion gases, some of the carbon black raw material being burned and the rest being converted into carbon black and tail gas by thermal cracking. Hydrocarbons with a highly aromatic composition, such as coal-tar oils, ethylene cracker residues and other petroleum products, for example, are used as carbon black raw materials.
The carbon black raw material is normally sprayed or injected into a mixing chamber formed as a narrow point to achieve intensive mixing of the carbon black raw material with the hot combustion gases as a result of the great turbulence of combustion gases prevailing there. This mixture then enters the carbon black reaction chamber, which normally has a broader cross-section than the narrow point. The actual carbon black formation process, consisting of nucleation followed by growth of the carbon black nuclei, takes place in this reaction chamber and is stopped downstream by spraying in water. All reactor components consist of a steel shell with an inner lining of ceramic material.
The physical and chemical processes that take place during carbon black formation are very complex. The heat of the combustion gases is very quickly transferred to the atomized droplets of the carbon black raw material and leads to more-or-less complete evaporation of the droplets. Some of the evaporated carbon black raw material is burned in the excess combustion air. Under these conditions, the molecules of the carbon black raw material are dehydrated and form carbon black nuclei. Nucleation is substantially restricted to a limited spatial area, the nucleation zone, inside the reaction chamber directly behind the mixing chamber. In the downstream area of the reaction chamber, the carbon black nuclei grow to form spherical or needle-like primary particles. The primary particles in turn combine under the reactive conditions in the reaction chamber to form larger aggregates, firmly bonded to each other. The way in which the particles combine is generally described as the structure of the carbon black.
The factors that substantially influence carbon black formation are the air or oxygen excess in the combustion gases, the temperature of the combustion gases and the reaction or residence time from the mixing of the carbon black raw material into the combustion gases to the stopping of the reaction by quenching with water, which is sprayed into the downstream area of the reaction chamber using a quenching nozzle.
The temperature of the combustion gases is normally set to a value of 1200 to 1900° C. The higher the temperature, the smaller the carbon black aggregates formed. The residence time also influences the aggregate size distribution. It can be adjusted in known carbon black reactors by means of the flow speed and positioning of the quenching nozzle to 1 ms to 1 s.
The stated carbon black production process is known from Ullmanns Enzyklopädie der technischen Chemie 4th Edition, Volume 14, pages 633 ff (1977) (in German) and from Carbon Black, Science and Technology, Verlag Marcel Dekker, Inc., New York 1993.
The known process has the disadvantage that the colour depth of the furnace blacks can only be obtained by costly post-treatment outside of the furnace reactor.